Is infra red radiation all there is to "heat"?

Factual Questions
1

So this is probably a “duh” question, but is heat nothing but infra red radiation? For example, the heat from hot water, flame, molten lava, is it all caused by the same infra red radiation, or is there something else involved?

How about other effects that feel like heat? (Say chemical or other types of radiation). Do they feel “hot” because they somehow put out infra red radiation, or is it just perception that makes them “feel” hot, but they really aren’t? For example, a chemical burn, is it really puting out heat or is it just perception and no actual heat is generated?
In other words, (back to the original question) is heat = infrared radiation and vice versa at all times, or is something else involved?

2

I thought “heat” was the increased motion of atoms and molecules in a solid or fluid, and that infrared radiation was merely a means of causing this increase in motion.

3

The classic description is that heat = molecular motion - when something gets hotter, the molecules vibrate more vigorously.

Molecules in motion tend to emit radiation, much of which is infrared (though it can be visible radiation when the temperature gets high enough). Heat can also be transferred by conduction and convection (circulation of a heated liquid or gas).

4

hmmm… ok maybe Im asking two questions there. Forgot about molecular motion = heat.
What I’m trying to find out specifically is if the radiation that is emitted by heat is SOLELY infrared. So the energy part of “heat” that radiates outward, is it infra red alone or is there something else?

5

As I understand it, all objects emit electromagnetic waves; at the temperatures we normally think of as “warm” and “hot,” this is almost entirely infrared radiation. If an object gets hot enough, it starts to glow with visible light – red, then orange, yellow, white, etc. Eventually it’ll go on up into ultraviolet, x-rays, gamma rays … but that would have to be pretty darn hot.

So at normal temperatures for us, it’s pretty much all infrared, yeah.

6

Electromagnetic radiation of any wavelength can produce the molecular motion that we call heat. That includes radio waves, microwaves, infrared and visible light through ultraviolet, X-rays and gamma rays. Infrared light gets called ‘heat’ a lot because, as chorpler said, objects at usual earthly tempereratures emit most of their excess energy at infrared wavelengths. As the temperature of an object increases it emits radiation at shorter and shorter wavelengths. The relation between temperature and the wavelength of emitted radiation is described in this Wikipedia article: Black body radiation

7

As far as I can tell, heat is that form of energy that raises the temperature of objects.

For example, an electric motor takes in electrical energy and delivers mechanical energy and all of the input electric energy that doesn’t come out as mechanical energy is heat. That heat raises the temperature of the motor and the device it is driving as well of the object to which the mechanical energy is delivered.

The temperatur of all of those things rises until the heat energy into them is all delivered to the environment via radiation (usually IR unless the objects get hot enough to glow), convection and conduction. Ultimately all of that heat energy is distributed into the earth and its atmosphere, raising the earth’s temperature slightly. This results in a slightly increased radiation from the earth into the surrounding interplanetary space and so on and so on.

8

I guess it would be well to add that temperature is a measure of the kinetic energy of the molecules in the objects to which the heat energy is delivered.

9

In addition to being a form of energy that adds kinetic energy to the molecules, it also adds potential energy to solid objects in expanding them against the force of cohesions between molecules.

10

Hot (that is to say, above absolute zero) objects can produce electromagnetic radiation at any frequency (in fact, all objects produce all frequencies, to some degree), and any frequency of radiation (in fact, any kind of radiation at all, not just electromagnetic) will heat an object it hits if it is absorbed. The Sun produces visible light in exactly the same way that your body produces infrared, and it’s mostly that visible light which warms you when you’re in a sunny spot.

11

I’m far from an expert on chemical burns but I think the term “burn” arose because some chemicals enter into chemical reactions with skin cells and damage them in a manner similar to a burn from excess heat. There might be heat released by such a chemical reaction that causes additional cell damage.

12

Infrared is not the only mechanism for heat transfer, if that’s what you mean. If you hold your hand over molten lava, most of the heat you feel is transferred by infrared. But there’s also some visible light, if the lava is glowing red. And there’ll definitely be convection (heat transfer through movement of hot air). If you hold your hand above a tub of hot water, in addition to infrared and convection, there’ll be steam generated by the hot water and coming in contact with your hand.

Thermos bottles are designed to minimize both convection and radiation. It’s a double-layer bottle with vacuum between the two layers, so there’s no air to transfer heat (no convection). And the surfaces are coated with shiny metal, which minimizes infrared radiation. Hot beverages aren’t hot enough to produce a significant amount of shorter wavelength radiation (visible light, UV, etc).

13

ok, so would it be safe to say that a hot tub or thermal pool is irridating infra red radiation? That is, that the energy felt as heat is in fact infra red?
Assuming that there are no chemicals involved in the picture. Just hot water.

14

Didn’t I just answer this? If you are standing by a hot tub, the heat you feel is infrared, convection (hot air) and steam. All three. Everything else is negligible.

15

This is far from a “duh” question. It is an incredibly profound one, and by asking it, you join the ranks of some of the greatest scientists in human history. Pretty much all of the underpinnings of chemistry and physics comes from a list of people who asked the same question, albeit phrased a little differently.

You mustn’t confuse “Heat,” with “Temperature.” They are not interchangable terms. “Heat” is a form of energy. “Temperature” is an arbitrary value (value scale, actually) used to specify how much heat energy something has.

There’s basicaly two things in the Universe; matter and energy. Matter is something we are all familiar with. It’s basically “stuff.” Cars. Comic books. Linoleum. The Sun, etc…
Energy is not so easy to relate to. You can’t see it, or taste it, or smell it, or feel it.
You * can* feel, hear and see its effects when it interacts with matter however.

And that’s what makes things so interesting: Energy can interact with matter. If it didn’t, things would be mighty boring.

Just like there’s different kinds of matter, there are different kinds of energy; electrical (think of lightning), mechanical (think of a water wheel), chemical, and most important, heat. The classic definition of energy is * something that has the capacity to do work*. Not really satisfying, but hey, that’s science for ya :rolleyes:

Anyway, energy can interact with matter. Three things can happen; matter can absorb energy, it can release energy, or-most importantly- it can convert one form of energy into another. Fireflies convert chemical energy into light energy. Prehistoric plants converted solar energy into chemical energy in the form of coal. Burning the coal converts it to heat energy which in turn is converted into mechanical energy by a turbine which turns the generator which in turn converts the mechanical energy into electrical energy, and on and on…

OK. Back to the OP. “Heat,” is just another form of energy currency. When matter absorbs it, the constituent molecules of said matter, which typically vibrate, will vibrate a little faster (or a lot faster, depending on the amount of heat we’re talking about). Again, this is a matter/energy interaction converting heat energy into vibrational energy. “Temperature” is a quantitative way to express the mean vibrational energy of a chunk of matter, and therefore, how much heat energy it contains.

Got it? Heat does not equal temperature.

This interaction cuts both ways, though. Matter can release this vibrational heat energy by converting/emitting it as another flavor of energy- electromagnetic energy. Depending on the amount of heat energy, the emitted electromagnetic radiation will span a discrete (but not finite) region of the electromagnetic spectrum. This is the “Black Body” radiation mentioned by others. Stuff at room temperature emits most of this energy in the infra-red region of the electromagnetic spectrum.

Other matter can in turn absorb this radiation, converting it back into molecular vibration (i.e. heat) energy. If it is your skin which is absorbing this radiation, the increased atomic vibrations are converted to chemical gradients/signals which are interpreted by your brain as heat.
It’s just that simple.

So is “Infra-red radiation.” One can be converted into the other through interaction with matter

16

Scrub this line. forget I ever wrote it.

I will preview. I will, I will, I will